I believe it's best to get a clear understanding of the situation by openly listening to the customer, honestly assessing if you are able to assist them or if the problem is beyond your support. If you able to assist them, inform the customer that you will do everything in your power to ensure satisfaction, and if you are not able to assit them ensure the customer that you will research the proper support and work with them to satisfaction. Patience and honesty is the best approach, stay calm, caring and professional at all times. Allow the customer to feel that you are partnering with them to meet their needs. Put yourself in their place, they will appreciate your support.